Excited-State Relaxation and Förster Resonance Energy Transfer in an Organic Fluorophore/Silver Nanocluster Dyad

Abstract

A single-stranded DNA-based (ssDNA) dyad was constructed comprising 15 silver atoms stabilized by a ssDNA scaffold (DNA-AgNC) and an Alexa 546 fluorophore bound to the 5′ end. The Alexa 546 was chosen to function as a Förster resonance energy transfer (FRET) donor for the AgNC. Time-correlated single photon counting (TCSPC) experiments allowed unraveling the excited-state relaxation processes of the purified DNA-AgNC-only system. The TCSPC results revealed slow relaxation dynamics and a red shift of the emission spectrum during the excited-state lifetime. The results from the model systems were needed to understand the more complicated decay pathways present in the collected high-performance liquid chromatography fraction, which contained the dyad (37% of the emissive population). In the dyad system, the FRET efficiency between donor and acceptor was determined to be 94% using TCSPC, yielding a center-to-center distance of 4.6 nm. To date, only limited structural information on DNA-AgNCs is available and the use of TCSPC and FRET can provide information on the center-to-center distance between chromophores and provide positional information in nanostructures composed of AgNCs.

Disentangling optically activated delayed fluorescence and upconversion fluorescence in DNA stabilized silver nanoclusters

“…Therefore, it is very likely that long wavelengths preferably select frozen conformations with a low energy of the dark state which then leads to a lower energy gap between the emissive and ground state (several scenarios are possible to achieve this). In solution the spectral relaxation should be free (no conformational freezing) and hence only limited by the time the molecule spends in the dark and excited states 25–27. To test our hypothesis and demonstrate the difference between the solution and PVA case, UCF spectra were recorded for varying excitation intensities at a fixed wavelength of 800 nm (Fig.…”

“…3C. It is important to reiterate that the spectral relaxation in solution (on the nanoseconds and slower time scale) results from conformational changes of the DNA scaffold upon charge redistribution in the dark and emissive state 25–27. The fast electronic spectral relaxation, accounting for the majority of the Stokes shift, happens on a sub-picosecond timescale and is not being discussed here 13,15,19,20.…”

Unusually large fluorescence quantum yield for a near-infrared emitting DNA-stabilized silver nanocluster

“…In order to shed light on the relationship between DNA sequence and the optical properties of DNA-AgNCs, we have in recent years focused on studying the photophysical properties of HPLC-purified DNA-AgNCs; this step of purification ensures that a single type of emissive DNA-AgNC species is studied. [6][7][8][9] Recently, crystal structure data of DNA-AgNCs has appeared in the literature, which will become a key part in understanding the relationship between DNA sequence and optical properties of the DNA-AgNCs. 10,11 In this paper, we have studied the photophysical properties of a NIR-emitting DNA-AgNC, stabilized by the sequence 5 0 -CCCGGAGAAG-3 0 .…”

Simultaneous Increase in Brightness and Singlet Oxygen Generation of an Organic Photosensitizer by Nanocrystallization

“…Excitation and emission spectra are independent of excitation wavelength for both nanoaggregates and nanocrystals, revealing that there is only one type of emitter in the samples (Figure S5, Supporting Information). To further explore the homogeneity of the nanoaggregates and nanocrystals, single particle fluorescence spectra of individual particles were measured using a confocal fluorescence microscope . The results show that the individual particles in nanoaggregates and nanocrystals have PL spectra similar to that of the bulk, confirming the homogeneity of samples at single particle level (see Figures S6 and S7 in the Supporting Information for details).…”